A mashup is a website or web application that seamlessly combines content from more than one source into an integrated experience.
Content used in mashups is typically sourced from a third party via a public interface or API. Other methods of sourcing content for mashups include Web feeds (e.g. RSS or Atom) and JavaScript.
Many people are experimenting with mashups using eBay, Amazon-com, google, Windows Live, and Yahoos APIs
So far, mash-up business models don't extend beyond running a few Google ads and collecting fees for sending buyers to e-commerce sites. One reason is that most Web sites don't allow for-profit use of their data by outsiders. But as traffic to mash-ups grows, companies may cut deals -- especially if mash-up sites spur new markets. Map-based mash-ups, for instance, might finally attract ultra-local businesses to advertise on the Web.
see software Ajax
Articles about mashups: